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PHYSICAL DATA ORGANIZATION

RAID SYSTEMS

Advanced Database SystemsDr. Fatemeh Ahmadi-Abkenari

September 2013

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RAID Systems

Redundant Array of Independent/ Inexpensive Disks

A lower level approach to the performance bottleneck caused by

disk I/O

Characteristics:

Increasing the availability of data in crash time Better throughput than a single disk Concurrent handling of multiple request Improving the request involving large block of data Transfer time reduction

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RAID Systems

Terminology:

Mirroring Striping Chunks 3- The unit of data to be spread

2- Spread of data across an array of disks1- One type of redundant storage

RAID LEVELS:

BASIC LEVELS (0, 1, 3, 5) HYBRID LEVELS (01, 10, 03, 30, 50, 100, …)

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RAID Levels

Level 0

Level 0: Uses only Striping and no Redundancy A failure of a single disk is devastating

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RAID Levels

Level 1

Level 1: Uses no Striping and only Mirroring High durability Expensive for many applications

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RAID Levels

Level 3

Level 3: Uses Striping and a type of Redundancy Chunks are at byte level The (n+1)st disk is the Parity disk Parity disk stores the XOR of the corresponding

bytes on the other n disks High transfer rate Useful for application with real-time requirement

a b c = a XOR b

0 0 0

0 1 1

1 0 1

1 1 0

b c a

0 0 0

1 1 0

0 1 1

1 0 1

a b c d = a XOR b XOR c

0 0 0 0

0 0 1 1

0 1 0 1

0 1 1 0

1 0 0 1

1 0 1 0

1 1 0 0

1 1 1 1

RAID Levels Level 3

A1: 1 1 0 1 0 1 1 0A2: 0 1 1 1 1 0 0 0A3: 1 1 1 1 1 0 1 0

Ap (1-3): 0 1 0 1 0 1 0 0

RAID Levels Level 3

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RAID Systems Level 5

Level 5: Uses Striping and Redundancy Stores Parity information No single parity disk

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Hybrid RAID Systems

Level 10

Level 10:Combination of Level 0 and Level 1

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Hybrid RAID Systems

Level 01

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Hybrid RAID Systems

Level 30

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Hybrid RAID SystemsLevel 03

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Hybrid RAID Systems

Level 50

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Level 100

Hybrid RAID Systems

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Cylinder

Track

Spindle

Platter

Sector

Arm Assembly Read/Write Head

Disk Organization

Disk Organization

A: TrackB: Mathematical SectorC: Disk Sector (Data Unit)D: Cluster

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Disk Organization

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Disk OrganizationTerminology:

Page: The unit of data transferred with each I/O operation

Block: is a sequence of adjacent sectors on a track

Cache: An array of page-size buffers in main memory

Hit: If an application refer to an item in a page exists in cache

Trade-off

Choosing the number of sectors in a block (page size)

For Further Reading;

Database Systems, An application-Oriented Approach

Second EditionChapter 9

Michael Kifer, Arthur Bernstein, Philip M. LewisPearson, Addison Wesley Publication

2006